A method and an apparatus for calculating the separation time of the arcing contacts of a high-voltage switchgear which is operatively coupled to a synchronous switching device and to an auxiliary switch having auxiliary contacts operatively connected to the arcing contacts. During execution of a predefined test condition the separation time of the arcing contacts and of the auxiliary contacts is measured. The time delay between the measured separation time of the arcing contacts and of the auxiliary contacts is calculated. Upon separation of the arcing contacts under an operating condition other than the predefined test condition, the separation time of the auxiliary contacts is measured. Then, the separation time of the arcing contacts is calculated as the difference between the separation time of the auxiliary contacts measured during the operating condition other than the predefined test condition and the calculated time delay.